1. Field of the Invention
The present invention relates generally to devices for the detection of particles and electromagnetic (EM) radiation and to methods for the manufacture of such devices. The present invention relates more specifically to methods for the more efficient manufacture of detection tubes using detection materials that require electron scrubbing to form an optimal detection device. The system provides electron scrubbing in a generally closed environment as part of the manufacturing process.
2. Description of the Related Art
Various types of particle and EM radiation detectors (such as neutron detectors) depend upon the use of plates or surfaces of materials sensitive to the particles or radiation to be detected. Making such detectors operate in an optimal manner typically means manufacturing the material plate or surface to a very high level of uniformity and purity. The removal of surface contaminants becomes an important part of the manufacturing process. This process for removing contaminants from the sensitive detection surfaces and plates is often carried out using electron scrub guns. Such scrub devices excite the material to the point where contaminants and impurities are displaced from the surface and drawn away to be removed from the detector or to be held in a non-interfering position within the detector.
The typical contaminant removal process is a scrub then seal process where the scrubbing is carried out before or during a vacuum process and then the chamber within which the detector material is positioned is closed and sealed. This can be an expensive and complex manufacturing process often requiring highly sophisticated vacuum and exhaust chambers. Frequently the manufacturing process is slow with the scrub then seal steps operating on only one or a very few detector tube assemblies at a time.
Traditional detectors that require electron scrubbing would be typically manufactured in an open configuration before processing and sealing. This manufacturing configuration, primarily required by the manner of electron scrubbing, involves a large open area that exposes the entire set of active detector components. This results in a much greater threat to the quality of the detector derived from the manufacturing process whereby exposure of the detector internal components to particles generated during processing occurs. Detectors are generally high voltage devices with close parts spacing, and therefore the presence of particulate contamination results in a higher frequency of static discharge and high voltage arcing during operation.
Typical prior art electron sources (electron scrub guns) must be placed several inches away from the surfaces they are intended to activate or clean. This is due to the general emission shape of the electron stream which may be characterized as emitting from a point source or small area. The further the separation (throw distance) between the electron source and the surface to be cleaned, the wider the spread of the electron stream. To create a relatively uniform stream of electrons, the traditional electron source must be positioned further back from the detector plates being scrubbed to impart a uniform flux to the edges of the detector relative to the center of the detector. In many cases, this effect under-processes the detector peripheral areas while over-processing the detectors central area where the electron flux is greater. This uneven scrub often leads to detector image defects, such as darker, less responsive outer regions, if the overall detector is not sufficiently activated or scrubbed.
In contrast to electron scrub guns, electron emitting plates produce a much more uniform stream of electrons, which can be used to more uniformly scrub, or activate a detector's surface. It is also possible to position such an electron source closer to the detector surfaces that are being scrubbed during the detector activation and manufacturing process. In other words, the use of electron generating plates reduces the need to create separation between the emitter plate and the detector surface being activated or cleaned. The work done by an electron scrub source is a function of its flux (quantity of emitted electrons) and voltage separation between the electron generating plate and the surface to be cleaned or activated. The emission flux of an electron generating plate (or a stack of generating plates) used to clean surfaces in a vacuum is adjustable by varying the applied voltage separation between the generating plate and activation surface, as well as varying the number of electron generating plates placed in a series configuration in proximity to the detector plate or plates.
It would be desirable, therefore, to have a detector tube device, and a method for manufacturing the same, that were capable of utilizing electron generating plates as the electron scrub source so as to improve the manufacturing process and reduce the incidence of particle contaminants within the detector, and to further reduce variations in the quality and character of the detector plate surface after scrubbing. It would be helpful to configure the manufacturing process for a detector tube stack into a smaller space that requires fewer ancillary mechanical parts and hardware to draw a vacuum and then perform a sealing operation with the vacuum or near vacuum in place. It would be desirable to eliminate as many sources of significant particle generating hardware from the overall manufacturing system. It would be desirable to position and place the electron scrub source in close proximity to the detector plate(s) to be scrubbed, thereby again minimizing the space required for the manufacturing process and the number and size of the components required.